Field of the Invention and Related Art Statement
The present invention relates to an electronic endoscope apparatus which utilizes a horizontal drive clock signal with a given frequency for solid state imaging devices having different numbers of picture elements.
Image pickup apparatus using solid state imaging devices such as CCD (charge coupled device) and the like have recently been used in a wide range of applications.
Electronic endoscopes (referred to as "electroscope" hereinafter) using solid-state image pickup devices such as CCD and the like to convert images to electrical signals for transmission have been brought into practical use in the field of endoscopes in place of conventional endoscopes (referred to as "fiberscope" hereinafter) which utilizes optical image guides for transmitting optical images.
The versatility of application of endoscopes and electroscopes and the variety in size and shape terms of the regions into which they are inserted has lead to the development of endoscopes with insertion portions of various sizes and shapes in accordance with the intended application. Thus, the solid state imaging devices which are mounted at the ends of the insertion portions of electroscopes have different sizes, i.e., different numbers of picture elements, in accordance with the types of endoscopes being used.
An endoscope apparatus of the prior art comprises an electroscope of the above-described type, a signal processing unit, a monitor unit and a light source unit and involves the problem that only electroscopes using solid-state imaging devices of the same kind and specification can be used because the drive circuits and the signal processing circuits for the solid-state image pickup devices are fixed.
In consideration of the aforementioned problem, the assignee of the present invention applied for a patent as disclosed in Japanese Patent Laid-Open No. 164433/1987 in which individual electroscopes containing an oscillator and a driving pulse generating circuit are made capable of being connected to a common apparatus body before use. This invention involves a problem, however, in that the size and cost of each of the individual electroscopes are increased because each of them has to contain an oscillator and drive circuit.
The assignee also applied for a patent as disclosed in Japanese Patent Laid-Open No. 213387/1987 in which a detachable drive pulse generating unit is used in an apparatus body that accommodates a video processor so that scopes incorporating different types of solid state imaging device can be used with a common apparatus. This invention, however, requires the preparation of various units corresponding to the various type of scope and, when many kinds of scopes are used, the management of these units becomes a complicated task, while the possibility that a unit which does not suit a particular scope may be mistakenly used is also involved. Thus some room for improvement still remains.
On the other hand, there is a problem in that the concentrations of impurities in channel regions for transmitting signal charges which are generated by the photoelectric conversion effected by photodiodes which comprises respective picture elements become non-uniform as the packing density of a solid state imaging device is raised. A driving method designed to deal with this problem was thus proposed in Japanese Patent Laid-Open No. 156962/1986. In this prior art, in a driving mode in comprising alternate periods of transmission of signal charges and periods of stoppage when there is no transmission of signal charges, a pulse with a low frequency is first input and transmission is then started during the transition from the periods of stoppage to the transmission periods. This allows black spot damage produced by the non-uniformity of a diffusion layer of impurities in the transmission channel to be reduced. In other words, individual solid state imaging devices having different numbers of picture elements sometimes involve problems that are unique to each, and, as shown in the example described in Japanese Patent Laid-Open No. 156968/1986. a situation can be envisage in which drive modes with subtle differences as between the respective devices will become necessary if these unique problems are to be solved.
A configuration was proposed in Japanese Utility Model Laid-Open No. 127167/1987 in which a driving pulse for an imaging device and a control signal for processing an image signal are produced by using PROM so that merely the changing the data of the PROM enables correspondence with any change in the specification of the imaging device or the apparatus which utilizes the device. In this invention, however, when an imaging device having a different specification is used, the PROM is changed to another PROM in which data in agreement with the imaging device used is written. Therefore, when this invention is applied to the field of the present application, the operation becomes complicated because the imaging device being used frequently has to be changed. In this invention, since the driving signal for the imaging device is generated by the PROM, the noise component produced by inputting an address for the driving of the PROM becomes mixed with the drive signal and thus in some cases produces fixed pattern noise in the image signal formed. In other words, when a plurality of address inputs are started or stopped, spike-like noise occurs in the power source line or signal line of a PROM IC, and thus a component with a frequency of 1/2.sup.n of the basic frequency of the driving signal produced by the PROM is superposed on the driving signal formed by the PROM, with the H and L levels of the drive signal being periodically changed. It is thought that the presence of a periodic change in level in the driving signal for the imaging device will have an influence on the efficiency of transmission of signal charges, and fixed pattern noise having the form of longitudinal stripes or a lattice form will occur in the resulting image.
A fiberscope equipped with a television camera containing a solid state imaging device has a function which is substantially the same as that of an electroscope, it is preferable to enable the fiberscope to be used in the same way as in the electroscope.